Portion of a toothbrush



FIG. 1 is a front view of the portion of a toothbrush showing our new design;

FIG. 2 is a right side view thereof, the left side view being a mirror image;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a right, frontal perspective view thereof; and,

FIG. 7 is a left, rear perspective view thereof.

The dotted lines are for purposes of illustration and form no part of the claimed design. 

The ornamental design for a portion of a toothbrush, as shown and described. 